1. Field of the Invention
The present invention relates to a thin film transistor substrate and a manufacturing method thereof, and more particularly, to an amorphous silicon thin film transistor substrate having a gate driver for an LCD panel and a manufacturing method thereof.
2. Description of the Related Art
A liquid crystal display (LCD) is one of the most popular flat panel displays (FPDs). An LCD generally includes two substrates, each having an electrode formed on an inner surface thereof, and a liquid crystal layer interposed between the two substrates. In an LCD, a voltage is applied to the electrode to re-align liquid crystal molecules and control an amount of light transmitted through the liquid crystal layer.
TFT-LCDs are now the most common type of LCDs. Electrodes are formed on each of the two substrates and thin film transistors (TFTs) are used for switching power supplied to each electrode. The TFT is typically formed on one side of the two substrates.
Generally, an LCD in which TFTs are respectively formed in unit pixel regions is classified as an amorphous type TFT-LCD and a polycrystalline type TFT-LCD. The polycrystalline type TFT-LCD has advantages in that it is capable of speedier operation at low power consumption. It has also an advantage in that TFTs for pixels and semiconductor devices for drive-circuits can be formed together.
On the other hand, the driving circuit for the polycrystalline type TFT-LCD further needs an annealing process for transforming an amorphous silicon into polycrystalline silicon after the amorphous silicon is deposited. In other words, in case that a glass substrate is used, a deformation in the glass substrate may occur during the annealing process. Also, since the gate driver has a structure of complementary metal oxide semiconductor (CMOS), both of n-channel transistor and p-channel transistor are formed on the same substrate. Thus, as compared with a manufacturing process of the amorphous type TFT-LCD in which a single channel type transistor is formed, a manufacturing process of the polycrystalline type TFT-LCD is more complicated and difficult.
In general, a substrate on which TFTs for an LCD are formed is manufactured by a photolithography process using a plurality of masks, and five or six photolithography process steps are used. Since the photolithography process is expensive, it is desirable to reduce the number of photolithography steps.